The present invention relates to a rotary drive system, more precisely it relates to a rotary drive system, which is capable of rotating an output shaft or a rotor on its axis.
An index table for machining works is known as an example of the rotary drive system. In the conventional index table, an output shaft is rotated on its axis by a motor and reduction gears, so that a rotary table, which is fixed to the output shaft, is rotated.
The rotary table is rotated through a prescribed angle for each machining step. To rotate the rotary table for precise positioning of the works, the rotational angle of the rotary table must be precisely controlled. The precise control of the rotary table is executed by controlling the rotation of the output shaft or the driving of the motor.
However, the above described conventional index table, for example, has a disadvantage. As described, the positioning of the works is executed by controlling the rotational angle of the rotary table or the output shaft. Even if the output shaft is rotated by a precise mechanism, it is unavoidable to make errors of rotational angle of the output shaft and the rotary table due to, e.g., backlash of the reduction gears. To make wide machining spaces, the works are located in the vicinity of an outer edge of the rotary table. Namely, the works are located separate away from the axis of the rotary table. Thus, said errors are enlarged at the positions of the works even if said errors are small for the output shaft, so that it is very difficult to raise the positioning accuracy of the works.